Gas-Phase Reaction Network of Li/MgO-Catalyzed Oxidative Coupling of Methane and Oxidative Dehydrogenation of Ethane

Abstract

A gas-phase reaction network involving reactive intermediates such as alkyl and alkyl peroxide radicals and alkyl hydroperoxides have long remained a mystery in oxidative coupling of methane (OCM) and oxidative dehydrogenation of ethane (ODHE) reactions. Herein we report direct observations of gas-phase reactive intermediates including CH2, CH3•, C2H5•, CH3OO•, C2H5OO•, CH3OOH, and C2H5OOH during OCM and ODHE reactions over Li/MgO catalysts with an online synchrotron VUV photoionization mass spectrometer connected to a catalytic reactor with adjustable distances between the catalyst bed and the sampling nozzle of the mass spectrometer. Secondary reactions of these reactive intermediates in the gas phase are elucidated, and the reaction network of OCM and ODHE reactions is established. These results greatly deepen the mechanistic understanding of OCM and ODHE reactions necessary for developing efficient catalysts and designing proper reactors.